So the Sense HAT library is provided with the Latin-1 character set built in, but it does give the user the option to provide their own text assets. If you look here you'll see the files named sense_hat_text.txt and sense_hat_text.png. The text file is used to index the order in which the characters appear in the png. Also the png is rotated 90 degrees to that every character is made up of continuous pixels.

If you were to re-create both of these files, and change their names to say sense_hat_greek.txt and sense_hat_greek.png and put them into /usr/lib/pythonXXX/dist-packages/sense_hat on your system, you would be able to load them like this:

However, because of how python deals with looping over strings you may run into issues with this part of the library where it expects one text character to equate to one png character. I believe a lot of Unicode characters are two bytes long, whereas everything in Latin-1 is one byte long.

The characters are 5x7 so it's even worse! I imagine they would be able to get something which looks better than Latin-1 but whether it would be easily readable is another question. Also one of the reasons we only went with Latin-1 in the first place.